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I agree with the comments of others here; the best approach would be to add a PA to the outdoor antenna tuning unit. Of course, to be sold commercially, it would need to be certified together with the main unit. I don’t really see any barrier to getting that configuration approved.
I think it would be practical to retain the design of the main unit mostly as it is, and pipe the RF output via coax to the outdoor ATU/PA. In this mode, you would disable modulation of the inside unit and send the RF and audio out to the ATU/PA on a cable, along with power and control signals. The ATU/PA would amplify the carrier to the 100 mW input level and apply modulation. The modulator could reside in the ATU, but I suspect there is probably plenty of audio available in the main unit such that additional amplification would not be necessary– especially if it were not modulating the PA of the main unit.
I haven’t seen the existing remote antenna, so can’t comment on whether the tuner would need to be modified, but I assume that it should be feasible to control it from the main unit over the cable.
To summarize, in order to be legal (and therefore certifiable), I would recommend adding a PA to the outdoor antenna tuner and sending the audio, RF, and control signals to it via cable.
You may well ask: why bother? You could just buy an outdoor transmitter instead, such as the Hamilton Rangemaster or the Chez Radio Procaster. That would work fine, but then you still have the need for an indoor unit to store the messages (for the Real Estate application). Having an external add-on unit that can simply adapt the Talking House to external operation would seem to be an ideal way to have a system that could be used either way. Also, the existing product is very simple to set up and operate, and requires no tweaking. That is essential for a non-technical user.
Now for those of you who like to experiment, as I do, there is absolutely nothing to stop anyone from building an outdoor ATU/PA as I have described and remoting the necessary signals to it. The only downside is that it certainly won’t be FCC Certified in that configuration. But if you are going to install it in compliance with Part 15 rules anyway, that should not be a problem. I am already thinking about building a remote PA for my TH once it arrives and I have a chance to gain some experience with it. It would sure be nice to have one of the existing remote antenna tuners to use as a starting point though.
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